1. Field of the Invention
The present invention relates to a fuel injector for supplying fuel into an internal combustion engine and more particularly to an orifice type fuel injector which injects fuel through orifices in an orifice plate.
2. Description of Related Art
In recent years, automobile emission gas regulations have been tightened and demand for reduction of harmful hydrocarbon components in emission gas from internal combustion engines has been growing. For reduction of hydrocarbon components in emission gas, it is useful to encourage atomization of fuel injected as a mist from a fuel injector mounted in a vehicle's internal combustion engine and it is also useful to suppress adhesion of fuel to the wall surface of the intake pipe by accurately orienting a fuel injection from the fuel injector toward a target point (an intake valve).
An orifice type fuel injector is available as a fuel injector which promotes atomization of injected fuel and improves the directivity of fuel injection. The orifice type fuel injector, which includes an orifice plate with orifices therein, causes the fuel to flow horizontally along the orifice plate and leads the horizontally flowing fuel into the orifices from which it is injected. Through this process, atomization of injected fuel is encouraged and a high directivity of fuel injection is achieved (for example, see Patent Document 1 and Patent Document 2).
The orifice type fuel injector has a problem that fuel injections from the plural orifices in the orifice plate and fuel atomization conditions are not uniform. This problem of nonuniformity is attributable to a guide portion which guides forward/backward movement of the valve to control fuel injections from the orifice plate.
The fuel injected from orifices in the orifice plate is first supplied as a valve side flow, a flow along the side of the valve. The fuel in this valve side flow passes through a fuel path which opens or closes as the valve moves backward and forward to leave or touch a nozzle body etc., and then flows down to the orifice plate and spouts out through the orifices. In this fuel supply structure, the valve is designed to move backward and forward to open or close the valve by sliding on a valve surrounding portion provided so as to surround the valve; and sliding of the valve is done through a guide portion formed by arranging plural sliding guides between the valve and the valve surrounding portion.
The fuel flowing down along the valve side as a valve side flow passes through the guide portion while it is flowing down. In this process, under the influence of the sliding guides, an eddy of the fuel occurs beneath the guide portion and under the influence of this eddy, nonuniformity in the flow velocity of the fuel flowing down toward the orifice plate occurs in the valve circumferential direction. If, as a result of this nonuniform flow velocity in the valve circumferential direction, the flow velocity of fuel injected from the orifices in the orifice plate should differ from hole to hole, fuel injections and fuel atomization conditions would be not uniform.
However, the problem of flow velocity nonuniformity in the valve circumferential direction attributable to the sliding guides normally occurs as a static flow velocity distribution in which high and low flow velocities are distributed depending on the arrangement of sliding guides. Therefore, the influence of flow velocity nonuniformity in the valve circumferential direction can be reduced by adopting a structure which matches the static flow velocity distribution. Patent Document 3 discloses a technique which takes advantage of this finding to make fuel injections from orifices and fuel atomization conditions uniform.
In the technique disclosed in Patent Document 3, unlike the conventional structure having a guide portion (sliding guide) on the valve, a guide portion is provided in a valve seat and plural orifices in a jet adjusting plate (orifice plate) are arranged in a way to match the arrangement of guides. In other words, the guide portion is located in the valve seat fixed with respect to the jet adjusting plate and thus the positional relation between the guides and the orifices in the jet adjusting plate is fixed, thereby offering a structure which matches the above static flow velocity distribution; and furthermore given this fixed positional relation, orifices are so arranged as to match the arrangement of guides, thereby offering another structure which matches the static flow velocity distribution. This reduces the influence of flow velocity nonuniformity in the valve circumferential direction.
Patent Document 1: Japanese Patent Laid-open No. Hei 11(1999)-200998
Patent Document 2: Japanese Patent Laid-open No. 2006-513371
Patent Document 3: Japanese Patent No. 3134813